Additional active ingredients are needed for use in aquatic systems in order to respond to new threats or treatment scenarios, enhance selectivity, reduce use rates, and to mitigate the risk of herbicide-resistance. Florpyrauxifen-benzyl is a new synthetic auxin developed for use as an aquatic herbicide. A study was conducted at North Carolina State University, in which 10 µg L−1 of 25% radiolabeled florpyrauxifen-benzyl was applied to the isolated shoot tissue of ten different aquatic plant species in order to elucidate absorption and translocation patterns in these species. Extremely high levels of shoot absorption were observed for all species and uptake was rapid. Highest shoot absorptions were observed for crested floatingheart [Nymphoides cristata (Roxb.) Kuntze] (A192 =20 µg g−1), dioecious hydrilla [Hydrilla verticillata (L.f.) Royle] (A192 =25.3 µg g−1), variable watermilfoil (Myriophyllum heterophylum Michx.) (A192 =40.1 µg g−1) and Eurasian watermilfoil (Myriophyllum spicatum L.) (A192 =25.3 µg g−1). Evidence of translocation was observed in all rooted species tested with the greatest translocation observed in N. cristata (1.28 µg g-1 at 192 HAT). The results of this study add to the growing body of knowledge surrounding the behavior of this newly registered herbicide within aquatic plants.

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Invasive emergent and floating macrophytes can have detrimental impacts on aquatic ecosystems. Management of these aquatic weeds frequently relies upon foliar application techniques with aquatic herbicides. However, there is inherent variability of overspray (herbicide loss) for foliar applications into waters within- and adjacent-to the targeted treatment area. The spray retention (tracer dye captured) of four invasive broadleaf emergent species: water hyacinth, alligatorweed, creeping water primrose, parrotfeather, and two emergent grass-like weeds: cattail and torpedograss were evaluated. For all species, spray retention was simulated using foliar applications of rhodamine WT dye (RWT) as an herbicide surrogate under controlled mesocosm conditions. Spray retention of the broadleaf species was first evaluated using a CO2-pressurized spray chamber overtop dense vegetation growth or no plants (positive control) at a greenhouse scale (GH). Broadleaf species and grass-like species were then evaluated in larger outdoor mesocosms (OM). These applications were made using a CO2-pressurized backpack sprayer. Evaluation metrics included species-wise canopy cover and height influence on in-water RWT concentration using image analysis and modeling techniques. Results indicated spray retention was greatest for water hyacinth (GH: 64.7 ± 7.4, OM: 76.1 ± 3.8). Spray retention values were similar among the three sprawling marginal species alligatorweed (GH: 37.5 ± 4.5, OM: 42 ± 5.7), creeping water primrose (GH: 54.9 ± 7.2, OM:52.7 ± 5.7), and parrotfeather (GH: 48.2 ± 2.3, OM: 47.2 ± 3.5). Canopy cover and height were strongly correlated with spray retention for broadleaf species and less strongly correlated for grass-like species. Torpedograss and cattail, while similar in percent foliar coverage, differed in percent spray retention (OM: 8.5± 2.3 and 28.9 ±4.1, respectively). The upright leaf architecture of the grass-like species likely influenced the lower spray retention values in comparison to the broadleaf species.

Four demonstration plots were selected at Roanoke Rapids Lake, NC to evaluate water exchange and aqueous herbicide residues in stands of submersed aquatic vegetation (SAV) following treatment with rhodamine wt dye and florpyrauxifen-benzyl to control monecious hydrilla. Florpyrauxifen-benzyl (Procellacor™ SC) was applied in combination with Rhodamine WT (RWT) at two of the plots. Dye measurements and herbicide residue samples were collected at specific time intervals to draw comparisons between herbicide and RWT dye dissipation. The two additional plots served as reference plots to the treatment plots. Pre- and post-treatment vegetation surveys were conducted to evaluate monoecious hydrilla control and non-target species response. RWT dye and herbicide residue data indicated rapid water exchange was occurring with each treatment plot. As a result, florpyrauxifen-benzyl concentration and exposure times (CETs) towards monoecious hydrilla were not sufficient to achieve adequate control by 4 weeks after treatment (WAT). To reduce the impact of hydraulic complexity and improve herbicide efficacy, treatments should coincide with minimal reservoir discharge events to extend herbicide CET relationships. Evaluations of florpyrauxifen-benzyl on late season, mature plants may have impacted herbicide efficacy. Evaluations should be conducted earlier in the growing season, on young, actively growing plants, to discern potential differences in efficacy due to treatment timing and phenology. More information on herbicide concentration and exposure time relationships for monoecious hydrilla should be developed in growth chamber and mesocosm settings to improve species selective management of monoecious hydrilla in hydrodynamic reservoirs.

Expanding the current aquatic herbicide portfolio, reducing total spray volumes, or remotely delivering herbicide using novel spray technologies could improve management opportunities targeting invasive aquatic plants, where options are more limited. However, research on giant salvinia [Salvinia molesta (D. S. Mitchell)] response to foliar herbicide applications at carrier volumes ≤ 140 L ha-1 is incomplete. Likewise, no data exists documenting S. molesta control with unoccupied aerial application systems (UAAS). Following the recent >100 ha incursion of S. molesta in Gapway Swamp, North Carolina, a case study was developed to provide guidance for ongoing management efforts. In total, three field trials evaluated registered aquatic and experimental herbicides using a 140 L ha-1 carrier volume. Select foliar applications from UAAS were also evaluated. Results at 8 weeks after treatment (8 WAT) indicated the experimental protoporphyrinogen oxidase inhibitor, PPO-699-01 (424 g a.i. ha-1), in combination with endothall dipotassium salt (2370 g a.e. ha-1) provided 78% visual control, whereas control when PPO-699-01 (212 g a.i. ha-1) was applied alone was lower at 35%. Evaluations also showed diquat (3136 g a.i. ha-1) alone, glyphosate (4539 g a.e. ha-1) alone, and metsulfuron-methyl (42 g a.i. ha-1) alone achieved 86 to 94% visual plant control at 8 WAT. Sequential foliar applications of diquat, flumioxazin (210 g a.i. ha-1), and carfentrazone (67 g a.i. ha-1) 6 wk following exposure to in-water fluridone treatments were no longer efficacious by 6 WAT due to plant regrowth. Carfentrazone applications made from a backpack sprayer displayed greater control than applications made with UAAS at 2 WAT deploying identical carrier volumes; however, neither application method provided effective control at 8 WAT. Additional field validation is needed to further guide management direction of S. molesta control using low carrier volume foliar applications.